1. Field of the Invention
The invention generally relates to the field of integrated circuit design, and more particularly to the design of a high-density deep-trench capacitor array, wherein a plurality of leakage sensor and switch devices are integrated so that capacitors with excessive leakage current can be detected and switched off to improve circuit reliability and yield.
2. Description of Background
Capacitor devices have been widely used in today's integrated circuits, such as phase-locked loop (PLL), charge pump, analog circuits, and electrostatic discharge (ESD) devices. As the silicon technology continues to advance and the number of on-chip devices continues to increase, high-density deep-trench capacitor arrays have been developed to provide switching current, reduce power supply noise, and protect signal integrity. However, as the dielectric film in the capacitor becomes thinner, the leakage current grows exponentially. Leakage current not only increases power consumption, but also jeopardizes power integrity and causes coupling and jitter problems for noise-sensitive devices such as PLL.
The leakage current of a capacitor generally increases as the operation time, temperature, and biased voltage increase. For instance, the measured leakage level of a good tantalum capacitor is in the range of 0.01 nA/μF·V. If the leakage current of a solid tantalum capacitor exceeds 10 nA/μF·V, it is generally considered defective and should be scrapped.
Many methods have been proposed to manufacture capacitors on chip. In U.S. Pat. No. 6,225,133, entitled “Method of manufacturing thin film capacitor,” a dielectric film made of materials with high dielectric constants such as Ta2O5, Bi4Ti3O12, and BaMgF4 is used to reduce the leakage of thin film capacitors. In U.S. Pat. No. 5,125,138, entitled “Miniaturized monolithic multi-layer capacitor and apparatus and method for making same,” various acrylates are used for the dielectric layers, with the number of layers ranging from a few to many thousands. In U.S. Pat. No. 7,193,262, entitled, “Low-cost deep trench decoupling capacitor device and process of manufacture,” a trench-type decoupling capacitor structure is added to a base logic design. Since the trench is made directly in the silicon wafer and the sidewalls of the trench are used for the capacitor dielectric, the planar area of trench decoupling capacitors can be made fairly small.